A semiconductor laser light source may be used mainly as a light source to be used for pumping a large output solid state laser. While a light source such as a xenon lamp is used for pumping the solid state laser in the related art, the output wavelength generally yields a broad spectrum, which reduces the laser pumping efficiency.
When the pumping is performed by using a semiconductor laser having a sharp wavelength spectrum instead of the light source such as a xenon lamp, lasing can be occurred on the solid state laser with the higher efficiency. A semiconductor laser element to be used as the light source for pumping the large output solid state laser must emit a laser beam at a several tens watt level. However, the output efficiency of the semiconductor laser element is the order of 50% under present circumstances. Therefore, heat is generated which is substantially equal to a laser optical output. Accordingly, in order to obtain a stable laser optical output, a cooling device is needed which cools the semiconductor laser element efficiently.
FIG. 23 shows a construction of the cooling device, which cools a semiconductor laser element in the related art disclosed in U.S. Pat. No. 5,105,429. The cooling device has a construction in which upper and lower lamellas 1 and 3 having paths through which cooling fluid, or fluid, flows, respectively, are laminated on and under a medium lamella 2 formed by an insulator such as glass.
An inlet opening portion 1A and an outlet opening portion 1B are provided for the cooling fluid in the lamella 1. Further, an inlet opening portion 3A and an outlet opening portion 3B are provided for the cooling fluid in the upper lamella 3. A path 1C, which is a path for cooling fluid, having one end communicating with the cooling fluid inlet 1A and the other end branching off to a front end surface 1a, is formed at the top surface of the lamella 1. Furthermore, paths 2A and 2B through which cooling fluid flows are formed in the medium lamella 2 by corresponding to the cooling fluid inlet 1A and the cooling fluid outlet 1B in the lamella 1.
A micro-channel (not shown) is formed at the bottom surface of the upper lamella 3, which communicates with the outlet opening portion 3B along a front end surface 3a and which has a smaller pitch than that of the path 1C. A semiconductor laser array 4 is joined at the top surface of the upper lamella 3 along the front end surface 3a. The micro-channel, not shown, is formed at the bottom surface of the upper lamella 3 and immediately under the semiconductor laser array 4. Here, the semiconductor laser array is defined as an array in which semiconductor lasers each having a light-emitting spot is formed horizontally.
The lower lamella 1, the medium lamella 2 and the upper lamella 3 are laminated and fixed by a bolt and a nut, which is inserted into center opening portions 1D to 3D formed thereon, respectively. The semiconductor laser array 4 is operated by a driving device 5, such as a direct current power supply.
In the cooling device in the related art, a single-crystal silicon (Si) substrate is used as a construction material for the lamellas 1 and 3. The micro-channel 1C and the micro-channel, not shown, of the lamella 3 are formed by using the photo-lithography technology and the etching technology such that they are typically 25 μm wide and 125 μm deep. Since it is difficult that a border layer is formed on a path wall in such a narrow micro-channel, the improvement of the cooling efficiency can be expected.
Since, in the cooling device 10 shown in FIG. 23, the micro-channel is formed on the silicon substrate by using the photo-lithography technology and the etching technology, expensive facilities such as an exposure device are needed, which causes a problem of expensive manufacturing costs.
Further, since the cooling device 10 has the silicon substrates, being used as the lamellas 1 and 3, or the insulator lamella 2, such as glass, which are mechanically weak, the cooling device 10 also has a problem in manufacturing yields.
Furthermore, since the lamellas 1 to 3 are mechanically weak, they cannot be fastened tightly when laminated. Therefore, even when a gasket, such as silicon rubber, is used for sealing between the lamellas, water may leak in operations for a long period of time.
The cooling device 10 in FIG. 23 has a problem that laminating the lamellas 1 to 3 increases electric resistance. In the cooling device 10, glass suitable for pasting silicon substrates constructing the upper and bottom lamellas 1 and 3 is used as the medium lamella 2. In addition, silicon rubber is sandwiched between the lamellas in order to seal the lamellas. Therefore, under this condition, it is impossible to electrically connect the lamellas 1 to 3 in series and then to drive the semiconductor laser array 4.
Accordingly, some measures for solving the problems are taken such as metallizing a metal film on the side wall surfaces of the lamellas 1 to 3, using a metal clip, and using conductive silicon rubber containing metal power as the gasket. However, the increase in serial electric resistance cannot be avoided, resulting in increase in Joule's heat generation.
Furthermore, the cooling device 10 in FIG. 23 does not use the other elements than the micro-channels efficiently. Therefore, there is a problem that the cooling efficiency cannot be increased significantly. In other words, in the cooling device 10, silicon is used as a material for the lamellas 1 and 3 in which the micro-channels are formed. However, the thermal conductivity of silicon is smaller than the thermal conductivity of metal. Therefore, it is difficult to remove a heat amount generated by the heat conduction through the lamellas 1 and 3.
Additionally, since glass is used as the medium lamella 2, the heat conduction by the medium lamella 2 itself does not operate very well.
Furthermore, a front end portion 2a of the lamella 2, which is made of glass, is thermally blocked from the other parts by a slot 2C. Therefore, the cooling performance of the front end portion 2a is significantly reduced.
Regardless of the construction, the front end portion 2a of the glass lamella 2 is positioned in the vicinity of the semiconductor laser array 4, which is provided on the lamella 3 thereabove. Therefore, the generated heat mostly reaches to the front end portion 2a of the glass lamella 2.
In other words, the cooling device 10 is designed especially to put a load only on the cooling fluid flowing path, which is formed in the lamella 3 in which the semiconductor laser array is provided. Thus, only the path must have a surface area required for cooling. Therefore, a finer path pattern has to be adopted.
However, such a finer micro-channel is expensive in processing cost, and the path is easily blocked with dust. As a result, the maintenance costs become higher, such as quality control over the cooling fluid.
FIGS. 24A to 24D are perspective diagrams showing an exploded diagrams showing the construction of another cooling device 20 in the prior art, which is disclosed in the Laid-Open Publication No. 1998-209531, and a perspective view showing the cooling device assembled as a semiconductor laser light source device. The cooling device 20 is formed by laminating plate-like members 21 to 23 made of metal such as copper and an alloy of copper with the higher thermal conductivity. An inlet opening portions 21A, 22A and 23A and outlet opening portion 21B, 22B and 23B for cooling fluid or fluid are formed in the plate-like members 21 to 23, respectively.
Each of the plate-like members 21–23 is typically 250 μm thick. Parallel channels 21C, which function as paths for cooling fluid, are formed 400 to 500 μm pitch, 130 μm deep, and 300 to 350 nm wide along a front end portion 21a on the top surface of the plate-like member 21. The channels 21C are shaped along ridges 21c. The ridges 21c extend toward the cooling fluid inlet 21A.
As a result, ridges 21D, which are converged from the ridges 21C toward the inlet 21A, are formed. That is, the cooling fluid introduced from the inlet 21A extends along the ridges 21D and is introduced to the ridges 21C, which are adjacent to the front end surface 21a. 
As shown in FIG. 24(d), the plate-like member 22 is laminated on the plate-like member 21 such that it can aligned with the opening portions 21A and 21B, which correspond to the opening portions 22A and 22B. Multiple through holes 22C are formed on the plate-like member 22 along a front end surface 22a by corresponding to the channels 21C on the plate-like member 21, respectively. As a result, the cooling fluid introduced to the channels 21C reaches to the upper side of the plate-like member 22 via the corresponding opening portion 22C.
The plate-like member 23 is provided on the upper side of the plate-like member 22. The plate-like member 23 can be obtained by providing and turning a member identical to the plate-like member 21 upside down on the plate-like member 22. Channels similar to the channels 21C and 21D on the plate-like member 21 are formed on the bottom surface.
However, channels corresponding to the channels 21D are converged to the outlet opening portion 23B. The cooling fluid flowing through the through holes 22C in the plate-like member 22 reaches to the outlet opening portion 23B from channels corresponding to channels 21C provided in the plate-like member 23 through the channels corresponding to the channels 21D.
In the cooling device 20 in the related art, which is shown in FIG. 24, paths in the plate-like members 21 to 23 are formed only by chemically etching channels, without the use of the lithography technology and/or the laser beam processing, for example. Therefore, the cooling device can be manufactured in the inexpensive manner.
Further, a material with higher thermal conductivity, such as copper or an alloy of copper is used as the material of the lamella member. Therefore, the load is not put only on the cooling fluid flowing paths, but a thermally integral structure having a larger thermal capacity can be formed.
In the cooling device 20 in FIG. 24, multiple through holes, which are independent from each other, are formed instead of the continuous slits 1C in the cooling device 10 in the related art, which is shown in FIG. 23. Therefore, the cooling device 20 is not divided into two areas, which are thermally blocked. Thus, the heat can be scattered and lost immediately from one area to the other area through a cross-linking portion between adjacent through holes.
Additionally, the path for cooling fluid is a channel having a larger section than that of the micro-channel. Therefore, the maintenance such as water quality control can be performed easily.
In the cooling device 20 in FIG. 24, channels are formed by using the chemical etching technology, and the cooling device 20 is essentially constructed so as to have a thermally integral structure by using metal members with the higher thermal conductivity. Therefore, the problem of putting loads only on the cooling fluid flowing paths, which is caused by the cooling device 10 in the related art in FIG. 23, can be overcome.
Nevertheless, the sectional dimensions of the channels 21C formed on the top surface of the plate-like member 21 along the front-end portion 21a and the channels 21D converging to the cooling fluid inlet 21A are defined by the thickness of the plate-like members. Especially, the depth of the channels is only about half of the thickness of the plate-like members. As a result, the paths still have fine dimensions. Therefore, the problem of blocking the paths with dust in cooling fluid is not completely solved, and the precise water quality control is still required.
The variation in the width and depth of paths formed by chemical etching causes the variation in path resistance in the multiple channels 21D. The cooling fluid introduced from the cooling fluid inlet 21A to multiple through holes 22C may not be distributed uniformly. Thus, the semiconductor laser array provided on the top surface of the lamella 23 may not be cooled uniformly in the longitudinal direction. In this case, the temperature difference in the semiconductor laser array is generated. The effect of the temperature dependency of band gap energy results in a problem of uneven output wavelength among semiconductor lasers, which construct the semiconductor laser array.
As described above, since it is difficult to have the large path section from the cooling fluid inlet 21A to the cooling fluid outlet 23B, the pressure loss in the cooling device 20 itself is increased. Therefore, the capacity of a feeding unit for feeding a desired amount of flowing cooling fluid is increased, which also increases the device cost.
It is an object of the present invention to provide a novel and useful cooling device, a semiconductor laser light source device including the cooling device and a semiconductor laser light source unit, which solve the problems in the cooling device in the related art.